The invention relates to a device for sucking a gas or a gas mixture and for mixing it with a liquid fuel flowing in a flow duct provided with walls, the device comprising: an intake duct and an outlet duct for the liquid, the ducts having first flow cross-sectional areas; a throttle section between the intake and outlet ducts, the throttle section comprising at least one elongate throttle duct for the flowing liquid fuel; and at least one gas duct, transverse to the center line of the throttle duct, which opens as a gas supply orifice to the throttle duct, the said throttle duct forming for the flow a second flow cross-sectional area, which is substantially smaller than the said first flow cross-sectional area, and extending with a substantially unchanging flow cross-sectional area from the said gas supply orifice to a downstream distance on the downstream side of the liquid flow.
Publications EP-0 417 776 and EP-0 607 166 describe devices which include in the flow-through duct for the flowing medium a plug which considerably reduces the flow cross-sectional area, whereby, as is known, the flow velocity is increased and underpressure is produced at the point of the rapid flow. The plug is hollow, and its wall has, at a distance from the narrowest point of the gap between the plug and the flow-through duct on the downstream side of the flow, a small orifice, whereby a supply passage is created for the additive via the hollow interior of the plug and the small orifice. The above-mentioned underpressure at the point of the rapid flow sucks the additive via the small orifice into the flowing medium. The purpose is to enable an additive to be introduced also into a medium having a high viscosity, such as a gel, and to enable an additive to be introduced into a flow of a medium having a high discharge resistance. It is possible that the device described in the publications works in some manner in the conditions mentioned above, but when the flowing medium is a fuel in liquid state, such as diesel oil, fuel oil, kerosene, or the like, the flow rate of which varies within a wide range and may additionally change suddenly, and the additive supplied is a gas, such as air or oxygen, considerable problems are encountered. First, if the device according to the publications is calibrated to supply a correct gas amount into a small liquid flow, the device will not suck a sufficient amount of gas into the liquid at a high liquid flow rate. Although the increasing of the liquid flow rate does somewhat increase the underpressure, and thus the amount of gas sucked in, the gas amount does not increase to a sufficient degree. As the liquid flow increases and its velocity increases, another problem is encountered, namely, the foaming of the liquid, for which liquid fuels have a tendency and which appears when the underpressure drops sufficiently low at the point of the small cross-sectional area, regardless of whether or not there is a sufficient amount of gas entering the liquid flow. Publication EP-0 607 166 additionally describes in the additive duct a valve the purpose of which is to control the amount of additive. This is, however, a one-way valve equipped with a straight valve disc, and the valve cannot serve to control the amount, since it has only two positions, open and shut. In a structure such as this, a disturbance in the steady flow of medium, such as its sudden decrease, which is usual or regular when the device is used in a liquid fuel flow, leads to a situation in which the medium flows backward into the additive duct and all the way to the one-way valve. The result is the blocking of the additive duct and/or the one-way valve.
Publications WO-96/15848 and DE-295 14973 U1 describe arrangements corresponding to that described above for introducing an additive, such as air, into diesel oil or fuel oil. In these publications, the structure of the device in the area of the liquid duct is precisely of the type discussed in the preceding paragraph, but they additionally have a device for drying the feed air in order to decrease the relative humidity of the air. Decreasing the humidity of the air does not in the least help to solve the problems described in the preceding paragraph.
Publication WO-93/12385 describes a device arranged in the fuel supply of a heating boiler in order to inject air into a liquid fuel so that a large, number of small bubbles are formed in it. For this purpose the device includes an air bubble device, of which there are presented as embodiments a jet pump (diffusion pump), a Venturi tube, and a flow duct provided with throttling. In the throttled flow duct the intake cross-sectional area is approximately equal to the outlet cross-sectional area, and the flow-through cross-sectional area between them is much smaller than the intake/outlet cross-sectional areas, and the smallest cross-sectional area is constant within a certain distance, which is a multiple of the corresponding diameter. It is seen from the figures that the air duct comes directly to the throttle duct, and that the apparatus does not include a one-way valve opening under a certain pressure. The purpose of the air bubbles is to improve gasification of the fuel in the oil burner. Such air bubbles may indeed work in the manner intended in the publication when used in a heating boiler oil burner, in which the burner nozzle supplies fuel into a furnace under atmospheric pressure or slight underpressure. In this case the fuel pump is required to produce only a relatively low pressure, in which case the air bubbles present in the liquid fuel will perhaps not badly disturb the operation of the pump. Furthermore, in the said use the liquid fuel flow is always constant during combustion, i.e. in heating boilers the control is always so-called two-point control, i.e. the burner either operates at full powerxe2x80x94in which case the fuel flow is always of a constant magnitudexe2x80x94or the burner is not at all in operationxe2x80x94in which case there is no fuel flow. When a combustion engine, such as a diesel engine, is concerned, it is necessary to supply fuel for very short moments, at a varying fuel flow rate and under a very high pressure, in which case the air bubbles, being compressible, cause uncontrolled changes in the fuel supply and spoil the operation of the engine. Furthermore, in a combustion engine a strongly varying flow tends to cause a back flow of fuel and, because of capillary effect, into the air ducts, where the fuel will block the small ducts, preventing further operation of the device, since the underpressure caused by the flow in the throttle is not, owing to the capillary forces, sufficient to remove the liquid fuel from the gas ducts. This problem is not solved by the construction according to the publication.
Publication EP-0 814 254 A1 discloses a mixing device for introducing air into fuel oil. The device does have an intake duct and throttle, and an air intake duct opening into it, but immediately on the downstream side there is specifically an expansion connected with the throttle, without any unchanging portion. The optimum value of the cross-sectional area of the throttle is defined as 2.5-3.8 mm2, and the optimum value of the cross-sectional area of the air ducts is defined as 0.013-0.025 mm2. The magnitude of the throttle in proportion to the intake/outlet duct, i.e. the desired underpressure, is not defined in the publication. The aim in the publication is specifically the foaming of the fuel oil which is arrived at by arranging the ratio of the cross-sectional area of the throttle to the cross-sectional area of the air ducts to be 100:1-290:1. The said expansion of the downstream side increases this foaming. The duct expansion is always open, and the air is introduced, in the case of one air duct, into the throttle directly from the same side on which it is taken from the outside. The publication also discloses embodiments having a plurality of air ducts, but in them air is supplied into the throttle from all of its sides. The objects of the publication, and the foam-like liquid fuel obtained thereby, do not work in a combustion engine, for the same reasons as stated above with respect to publication WO-93/12385.
One object of the present invention is thus to provide a device for sucking a gas or a gas mixture and for mixing it with a liquid fuel flowing in a flow duct provided with walls, in such a manner as to obtain in the liquid fuel, with practicable precision, the same gas content desired in the given case, regardless of the flow-through rate of the liquid fuel, at least when the flow-through rates are substantially variable. Another object of the invention is to provide a device of this type which would not produce foam in the liquid fuel flowing therein, or at least this foaming tendency would be minimal. A third object of the invention is to provide a device of this type, wherein the gas introduced into the liquid fuel within the throttle section would not have the tendency later to separate from the liquid fuel or this separation tendency would at least be minimal. A fourth object of the invention is to provide a device of this type, wherein the flow of liquid fuel into supply ducts for a gas or a gas mixture would be minimal in all operating situations in connecting with engines or burners or other devices using a liquid fuel. A further object of the invention is a device of this type, which would be simple and the operation of which would not require a control power source separate from the liquid fuel flow.
The disadvantages described above can be eliminated and the objects defined above can be implemented by means of the device according to the invention.
The following facts can be mentioned as advantages of the device according to the invention. Foam does not tend to be formed in the liquid fuel flowing through the device, and thereby disturbances in the supply of liquid fuel into its combustion chamber are avoided. Furthermore, in the device there is not a tendency for the liquid fuel to flow in a non-intended manner into the supply ducts for the gas or the gas mixture, and thereby disturbances in the flow of the gas/gas mixture are avoided, since the ducts intended for the gas/gas mixture remain cleaner of liquid fuel than in prior-known devices. With the help of the device of the invention, the specific amount of gas or gas mixture introduced into the liquid fuel will remain in it and will not tend to separate from the liquid fuel, wherein there is, of course, the restricting factor of the solubility of the gas/gas mixture in the liquid fuel. In prior-known devices, separation of the gas/gas mixture tends to occur even if the amount supplied ought to dissolve in the liquid fuel. By means of the device of the invention, air can thus be caused to dissolve in a liquid fuel, which thus remains a liquid and will not in any case turn into foam or gas. The device according to the invention can easily be supplemented and calibrated in accordance with the invention so that the amount of the gas/gas mixture supplied corresponds quite precisely to the desired concentration in the liquid fuel also at considerably different flow rates of the fuel, varying during operation. Furthermore, the device has the advantage that the device operates with merely the liquid fuel flow, in which case no control means driven electrically or with other pneumatics or other hydraulics are needed.